Biological Evolution and Culture

To draw a parallel between biological evolution, which changes a gene pool, and cultural evolution, which changes a group's social behavior, we need to think about selection in very general terms, the way we did in chapter 4, where we drew a parallel between natural selection and operant learning. Like those two, cultural evolution also can be seen as the result of variation, transmission, and selection. Cultural evolution, however, cannot be understood independently of the other two, because the behavior involved is operant behavior and depends for its acquisition on a genetic base stemming from natural selection.

Replicators and Fitness

What are the units of selection? What are the things that vary and are transmitted and selected? With natural selection and operant learning, we were able to avoid this question simply by talking about genes, alleles, and variation in operant behavior. With cultural evolution, the units of selection are less obvious and more controversial, because talking about culture in terms of behavior and selection goes against traditional accounts. What are the parts that make up a whole culture and enter into a process of selection?

To answer such questions, evolutionary biologists like Richard Dawkins (1989) developed the concept of a replicator, an entity that, once in existence, causes itself to be copied. (Even DNA cannot be said to “copy itself" because it only enters into a chemical process that results in a copy of the original.) To qualify as a replicator, Dawkins explains, the entity must possess three types of stability: (1) longevity, (2) fecundity, and (3) copying fidelity. Reproduction takes time; longevity ensures that the replicator stays around long enough to be reproduced. Dawkins imagines a gene, a piece of DNA, in a primordial “soup” that existed before there were organisms. The molecule or piece of molecule would have to be chemically stable long enough for a copy to be made, and the longer it lasted, the more copies might be made. After the advent of organisms, when genes in a gene pool tended to be chemically stable, they still could be changed by radiation or broken up during cell division—most importantly during the formation of gametes (meiosis) because gametes carry the copies that are passed on in offspring. Fecundity refers to the tendency toward frequent copying—of two rival replicators (alleles), the one that is copied more often will become more frequent in the gene pool. Copying fidelity refers to accuracy. Inaccurate copies tend to lose their parent's virtues. When replicators compete, the replicator that produces more faithful copies will tend to be more successful.

These three requirements favor small units, because a small piece of DNA is less susceptible to being damaged or falling apart, is quicker to copy, and has fewer possibilities for error. If nothing offset these considerations, replicators would always be the smallest possible. The requirements of stability are counterbalanced by other considerations that favor larger units.

The factors that promote larger replicators may be summed up in the word efficacy. A large unit can have a large effect on the phenotype (organism) in which it is positioned, and so it can have a large effect on its own future. If a single gene controlled the manufacture of one entire protein molecule—say, an enzyme that would in turn control several chemical reactions—it might ensure that its phenotype possessed traits that would lead it to live long and reproduce often.

Between the advantages of smallness (stability) and the advantages of largeness (efficacy), replicators tend to be intermediate and variable in size. Sometimes a relatively large piece of DNA might be stable enough to propagate through a population. Sometimes a small piece might be effective enough to be selected, if it controlled a crucial bit of structure in a protein molecule, for instance.

A particularly good way for relatively small units to achieve efficacy might be called “teamwork.” Dawkins points out that genes rarely operate on their own. Selection favors genes that cooperate or act in concert with other genes. Say two alleles of a gene, X and X, are matched in fitness on all counts except that X' works together with another gene Y to produce a more successful phenotype. The combination X'Y will flourish and possibly replace X-allele combinations altogether. This way, even large clusters of genes that work together can be selected—clusters that guide the development of clusters of traits, like lungs, breathing, skin, and sturdy limbs or feathers, wings, flying, and building nests in trees. Dawkins theorizes that this is how organisms came into existence; genes survived and reproduced better when they were packaged into “survival machines”

< Prev   CONTENTS   Source   Next >